This invention relates to herbicidal compositions and methods of use. In particular, this invention relates to herbicidal compositions comprising an herbicidally effective amount of a thiolcarbamate herbicide in combination with an extending amount of an extender compound. An extender serves to prolong the effectiveness of single or multiple applications of the thiolcarbamate herbicide in controlling undesired plant growth. The extenders of the instant invention are amides.
Thiolcarbamates are well known in the agricultural art as herbicides useful for weed control in crops such as corn, potatoes, beans, beets, spinach, tobacco, tomatoes, alfalfa, rice, peanuts, and soybeans among others. Thiolcarbamates are primarily used in preemergence application. They have been found to be particularly effective when incorporated into the soil prior to the planting of the crop. As a herbicide, the thiolcarbamate is most concentrated immediately after its application. How long thereafter the initial concentration is retained depends in large part on the particular soil used. Thus the rate at which the thiolcarbamate herbicide concentration declines following its application tends to vary from one type of soil to the next. This is evident in the observable extent of actual weed control after considerable time has elapsed.
The extender compounds of the instant invention extend the soil life of thiolcarbamate herbicides in soil which has been treated one or more times before with a thiolcarbamate herbicide or in soil which has had no previous treatment with a thiolcarbamate herbicide. Soil which has been previously treated with a thiolcarbamate herbicide is termed "pretreated soil"; whereas soil which has not been so treated is termed "non-pretreated soil."
Under certain environmental and other conditions, thiolcarbamate herbicides are degraded more rapidly in pretreated soil of certain types than in non-pretreated soil. Such pretreated soil is considered conditioned to degrade thiolcarbamates herbicides at an accelerated rate compared to non-pretreated soil.
The extenders of the instant invention prevent rapid soil degradation of thiolcarbamate herbicide. Not only do the extenders prevent the rapid soil degradation of thiolcarbamate herbicides in pretreated soil, but also prolong the herbicidally effective soil life of thiolcarbamate herbicides in non-pretreated soil.
The soil in many of the examples below showing activity of representative extenders of the instant invention has been pretreated. Such pretreatment is designed to simulate field conditions wherein a field has been repeatedly treated with a thiolcarbamate herbicide. This simulation is effected by retreating the experimental soil, employed herein within weeks of the first treatment rather than seasons later as in the fields. Such a short experimental retreatment period highly conditions the soil.
The improvement in the soil persistence of the thiolcarbamate herbicide effected by the extender compound can manifest itself in a variety of ways. Improved soil persistance can be shown by herbicidal efficacy tests, wherein the degree of weed injury is measured after a set period of time following application of the herbicide. In such a test, the extender compound is shown to increase the herbicidal effectiveness of the thiolcarbamate by increasing the persistence of the latter in the soil, and thus prolonging its effective life.
In order for a compound to qualify as an extender, it is highly desirable that the compound have no significant herbicidal activity of its own. Each of the amide extenders of the instant invention were screened for herbicidal activity, and each were shown to have no or negligible herbicidal activity.